As more people use antidepressants and excrete them into waterways, scientists are worried that residues of common medicines such as Prozac and Zoloft are harming aquatic life, according to recent studies.

Even when exposed to very small doses, shrimp become more active and quick. Freshwater snails have a harder time attaching to surfaces. Cuttlefish, prawns, and mussels experience color changes, and some spawn spontaneously, while minnows show signs of anxiety. Scientists warn that these changes are happening at even smaller concentration levels than previously thought.

University of Portsmouth marine biologist Alex Ford’s study on antidepressants and their impact on mollusks and crustaceans will be published this week in a special edition of the journal Aquatic Toxicology. Ford found effects on marine life can be seen at very low concentrations but said it’s difficult to prove the effects in the wild and emphasizes that all the studies done to date are laboratory studies.

Short of therapists and doctors talking to the fish about how they feel, spotting changes can be difficult.

"With antidepressants, very often the changes can be subtle behavioral changes which are hard to detect," said Ford. Compare that with experimenting on male fish with estrogen, and "it's a lot easier to see if a fish is changing sex than to detect abnormal behavior, when behavior can change very quickly."

How exactly can human medicines reach fish and other sea life? It’s simple. Antidepressants show up in urine, and wastewater treatment plants don’t yet have an inexpensive or widely adopted way to filter out drug residues. Some exciting progress has been made in that field, but implementation is far afield.

It’s been just over a decade since scientists first sounded the alarm that America’s dependency on antidepressants might be affecting fish and other marine life. Since then, the number of Americans who rely on antidepressants has grown substantially, and by 2011, nearly 250 million prescriptions a year were being filled.

It’s not solely antidepressants. In January, researchers with the Environmental Protection Agency published a study that looked at effluent from 50 large wastewater treatment plants in the U.S. and frequently detected active pharmaceutical ingredients. When it came to fish and marine life, they said, “results suggest closer examination of risks to fish and other aquatic life is justified.…”

No surprise that some studies confirmed that fish found closer to wastewater treatment plants showed higher concentrations of antidepressants, but it’s the never-ending stream of them into our waterways that makes the problem a persistent one, not just here but worldwide.

Scientists worry that fish and other aquatic life that are repeatedly exposed to medications that affect their behavior could lead to changes in the way they feed or reproduce, and they are concerned about how those effects may affect entire populations. One study showed exposed male minnows became more aggressive, while females produced less eggs.

"Fish do not metabolize drugs like we do. Even if environmental doses aren't thought to be much for a human, fish could still have significant accumulation, and as it appears, changes in their brain's gene expression," Rebecca Klaper, a professor of freshwater sciences at the University of Wisconsin–Milwaukee, told Environmental Health News.

Baylor University environmental science professor Bryan Brooks said that by 2050, seventy percent of the world’s population will live in urban areas, compounding the problem.

“People are living longer, and older populations take more medicines in developed countries,” Brooks said. His recent paper, "Fish on Prozac (and Zoloft): Ten Years Later," makes it clear there’s still much we don’t know about the effect of pharmaceuticals on marine life.

Improving wastewater treatment can be effective, especially in combination with wetlands, Brooks said.

“Wetlands have advantages over other technologies because they can provide less expensive options for wastewater treatment while providing other environmental services, such as habitat for wildlife,” he said.

Wetlands act as a kidney, filtering out pollutants that are taken up by plants. Constructed wetlands, placed near wastewater treatment plants, not only clean water and provide wildlife habitat but are often less expensive to construct than additional wastewater treatment plants, and they can handle fluctuating water levels.

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